1. Field of the Invention
The present invention relates to signal generator circuits, and, more particularly, to a modulation circuit configured with integrated microelectro-mechanical system (MEMS) components.
2. Description of the Related Art
Modern electronic devices often use microprocessors or other digital circuits which require one or more clock signals for synchronization. For example, a clock signal permits the precise timing of events in the microprocessor. Typical microprocessors may be supervised or synchronized by a free-running oscillator, such as driven by a crystal, an LC-tuned circuit, or an external clock source. Over the years, clocking rates have continued to increase, and currently clock rates in personal computes may exceed 2.0 gigahertz (GHz). As clock rates increase, the circuits generating and processing the clock signals are susceptible to generating and radiating electromagnetic interference (EMI). The spectral components of the EMI emissions typically have peak amplitudes at harmonics of the fundamental frequency of the clock circuit.
In order to comply with such government limits on EMI emissions, spread spectrum clock generation (SSCG), such as that disclosed in U.S. Pat. No. 5,631,920, has been used to reduce EMI emissions. In summary, an SSCG circuit may include a clock pulse generator for generating a series of clock pulses, and a spread spectrum modulator for frequency modulating the clock pulse generator to broaden and flatten amplitudes of EMI spectral components which would otherwise be produced by the clock pulse generator. The spread spectrum modulator frequency modulates the clock pulses with specific profiles of frequency deviation versus the period of the profile. Currently, for example, the SSCG clock signal is generated on the system printed circuit board by either a discrete clock integrated circuit (IC), or by a phase lock loop (PLL) that is integrated into one or more application specific integrated circuits (ASICs).